Many nozzle type devices are not necessarily used very frequently and consequently are susceptible to the build up of foreign matter inside the nozzles. Typically this may occur when, for example, nozzles used in fire fighting systems are located in areas where such contamination can arise.
In addition in commercial kitchens and the like nozzles are located above hot plates and these can become clogged with grease and block their use.
It is in fact known for insects such as wasps to build nests in nozzle orifices and also for dust and other matter to build up in these orifices. One solution has been to cap the unused nozzles. One such cap of a synthetic material, which fitted over the mouth of an existing nozzle, was found to deteriorate with time and to permit foreign matter to enter the nozzle.
Further attempts to solve the blocking problems a nozzle capping means was provided in the form of a nozzle tip having a metallic sealing membrane attached thereto by retaining means that sealed the membrane to the nozzle tip. This membrane was able to be perforated when flow through the nozzle commenced however the residual membrane attached to the nozzle after perforation acted to hinder the projected spray pattern once the nozzle began spraying.
In addition in order to permit perforation of a membrane at lower pressures the membranes need to be thinner and therefore less robust and more susceptible to environmental damage.